Such a method is described in L. Ciavaglia, N. Bouadallah, E. Dotaro and N. Le Sauze, “Matching Fairness and Performance by Preventive Traffic Control in Multiple Access Networks”, Opticom, Dallas, Tex., USA, October 2003.
A data network is used for transferring data from one place to another. For this purpose, the network comprises nodes, i.e. devices for receiving data from and/or for feeding data into the network, and data transfer lines connecting the nodes. The data transfer lines are called buses.
A data bus has a direction towards which the signals carrying the data move on the bus. The nodes are situated along the bus. A node may receive data originating from nodes located upstream, i.e. located in the direction where signals come from, and a node may send data to nodes located downstream, i.e. located in the direction towards which signals move on the bus.
A bus has a limited data transfer capacity, caused e.g. by the limited bandwidth of a channel. Therefore, when data is to be added to the bus at a node, the node needs free data transfer capacity on the bus to do so. Without any measures, nodes located at or near the upstream end of the bus have a relatively easy access to the bus, whereas nodes located at or near the downstream end of the bus may have difficulties to find data transfer capacity not already used by upstream nodes.
For this reason, a fairness mechanism may be applied. The fairness mechanism makes upstream nodes (i.e. nodes with respect to which further nodes located downstream exist) reserve data capacity for downstream nodes (i.e. nodes with respect to which further nodes located upstream exist). Then downstream nodes will find free data transfer capacity on the bus.
L. Ciavaglia et al. describe an access control mechanism for a multipoint-to point network, comprising a plurality of nodes only adding data to a bus, and a single node only dropping data from the bus. It uses a preventive anti-token mechanism to grant access to the bus. An anti-token forbids a node to emit data traffic for a given amount of time, thus preserving voids for downstream nodes. For every node, a fixed amount of data transfer capacity is reserved, according to a Service Level Agreement (SLA). So every node will find some free data transfer capacity of the bus. A node may also benefit from unused reserved data transfer capacity of upstream nodes.
The disadvantage of this known method is a large amount of unused data transfer capacity (i.e. bandwidth) on the bus, in particular near the upstream end of the bus. Only at the downstream end of the bus, its full data transfer capacity may be used.
It is therefore the object of the invention to improve said method to allow a better bandwidth utilization, and to use available resources more efficiently.